In 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution), it has been decided to support MBSFN in which multiple base stations are synchronized to perform MBMS (Multimedia Broadcast and Multicast Service) on the same frequency.
An MBSFN area (range in which multiple base stations are synchronized to perform the same MBSFN transmission) defined by LTE is composed of the following two types of cells (Non-Patent Document 1):                Cell in which a base station performs an MBSFN transmission (MBSFN transmitting and advertising cell: hereinafter termed an “MBSFN service cell”); and        Cell in which a base station does not contribute to an MBSFN transmission, but performs only a unicast or single-cell/multicast transmission is performed (MBSFN area reserved cell: hereinafter termed a “reserved cell”).        
Note that the terms MBSFN, unicast, and multicast include not only communications using MBSFN, unicast, and multicast respectively but also services using MBSFN, unicast, and multicast respectively.
Unicast transmission and MBSFN transmission are time-division multiplexed (TDM) on a per-subframe basis. For example, when ten subframes make up one frame and there are four MBSFN subframes, the remaining six subframes are unicast subframes.
In an MBSFN service cell, the subframes other than MBSFN subframes (subframes used for MBSFN transmission) are unicast subframes.
In a reserved cell, one of the following two types of control is performed when multiple other cells in the MBSFN area perform MBSFN transmission (MBSFN subframe transmission time period).
Decrease the transmission power and perform unicast transmission (for example, unicast transmission only to the terminals in the center of the cell is performed) or perform single-cell/multicast transmission; and
Do not transmit any data.
One of the purposes of this reserved cell, provided on the boundary with other MBSFN areas or unicast cells, is to reduce interference from outside the MBSFN area and to improve coverage and outage of MBSFN.
The transmission power or the maximum of the transmission power in a reserved cell is determined by the target value of the MBSFN outage and the MBSFN MCS (Modulation and coding Scheme) using, for example, a table (decision table) that is prepared in advance.
Note that an outage represents that a user does not satisfy a service requirement condition of a communication system and corresponds, for example, to a service condition that is equal to or lower than an outage threshold of an acceptable performance of the system. This outage threshold is the minimum performance index at which the system is considered to be in an operating state. For example, when a required error rate outage, that is, an outage probability, is used, whether or not a percent of users whose required error rate exceeds the outage probability is lower than x % (for example, 5%) of entire users is a criterion at which the system is judged to be in the normal operating state.
With reference to FIG. 24 and FIG. 25, a conventional method for determining a transmission power, or the maximum of the transmission power, of a base station in a reserved cell using a table prepared in advance will be described. As shown in FIG. 24, it is assumed that there is an MBSFN area that is composed of MBSFN service cells and reserved cells and that the MBSFN area is surrounded by neighboring unicast cells.
FIG. 25 is a diagram showing an example of a table used to determine the transmission power, or the maximum of the transmission power, of a reserved cell. As shown in FIG. 25, the relation (correspondence) among the outage probability (%) of the MBSFN required error rate, MCS, and the transmission power, or the maximum of the transmission power, of a base station in a reserved cell is prepared in the memory as a table. The values of the table shown in FIG. 25 have been calculated in advance through computer simulation.
First, the following describes how to interpret the table in FIG. 25. Although not limited thereto, it is known in the radio communication that the smaller the MBSFN MCS number is, the lower a modulation rate and a coding rate are and that the larger the number is, the higher the modulation rate and the coding rate are. For example, MCS 1 corresponds to QPSK (Quadrature Phase Shift Keying) and MCS 10 corresponds to 16QAM (Quadrature Amplitude Modulation).
When the transmission power, or the maximum of the transmission power, of a base station in a reserved cell is 100% (the ratio of the transmission power to the transmission power of an MBSFN subframe is 100%, and this is the maximum transmission power), the outage probability for MBSFN MCS 1 is 20% (20 terminals out of 100 terminals cannot receive MBSFN). The outage probability (%) is 40% for MBSFN MCS 2, and this corresponds to a situation in which 40 terminals out of 100 terminals cannot receive MBSFN. The outage probability (%) is 100% for MBSFN MCS 10, and this corresponds to a situation in which 100 terminals out of 100 terminals cannot receive MBSFN.
When the transmission power, or the maximum of the transmission power, of a base station in a reserved cell is reduced to 50%, the outage probability for MBSFN MCS 1 is 10% (10 terminals out of 100 terminals cannot receive MBSFN). The outage probability for MBSFN MCS 2(%) is 20%, and this corresponds to a situation in which 20 terminals out of 100 terminals cannot receive MBSFN. The outage probability (%) for MBSFN MCS 10 is 80%, and this corresponds to a situation in which 80 terminals out of 100 terminals cannot receive MBSFN.
When the power of a base station in a reserved cell is 0% (no data transmission), the outage probability for MBSFN MCS 1 is 0% (That the MBSFN outage probability (%) is 0% means that the percent of users (terminals) who cannot receive MBSFN is 0%). The outage probability (%) for MBSFN MCS 2 is 2%, and this corresponds to a situation in which two terminals out of 100 terminals cannot receive MBSFN. When the power of a base station in a reserved cell is 0% for MBSFN MCS 10, the outage probability (%) is 10% and this corresponds to the state in which ten terminals out of 100 terminals cannot receive MBSFN.
The MBSFN outage probability is determined based on the requirement condition for the quality of MBSFN that is actually transmitted, and, based on a volume of PTP (Point To Point) traffic in the reserved cell, the following are determined:                MBSFN MCS satisfying an outage probability; and        Transmission power, or the maximum of transmission power, for MBSFN subframes in a reserved cell (percent of MBSFN power) Note that PTP, which is equivalent to unicast, means a dedicated communication scheme or a service by the dedicated communication scheme.        
For example, if
the number of MBSFN subframes is fixed,
the target value of MBSFN outage probability is 10%, and
MCS is 2,
then, it is determined by the table in FIG. 25 that the transmission power, or the maximum of the transmission power, of a base station in the reserved cell is 10% of the maximum transmission power of MBSFN.
On the other hand, if a transmission rate of MBSFN is fixed, the number of MBSFN subframes is changed so that the number is inversely proportional to the MBSFN MCS value (normally, the smaller the value is, the lower the rate). When the MBSFN MCS value is small, the number of MBSFN subframes per frame is increased.